A charging method for an electrophotographic photosensitive member (photosensitive member) in an electrophotographic image forming apparatus may be a brush charging method. This charging method includes an electrically discharging method that uses an electric discharge generated between a charging brush serving as a charging member and a photosensitive member, and an injection charging method that electrically charges a photosensitive member by directly applying current from a charging brush to the photosensitive member.
A roll charging brush (hereinafter, also referred to as “roll brush”) used in the brush charging method may be fabricated by helically winding a base cloth, which is a strip-like base material having conductive fibers implanted, around a cylindrical metal core bar without a gap. If such a roll brush is used, a charge irregularity (hereinafter, also referred to as “winding-seam irregularity” of the photosensitive member may be generated because of a winding gap generated near a winding seam, which is a seam formed by mutually adjacent edges of the strip-like base cloth with respect to the core bar. Consequently, a density irregularity may be generated in an image. In particular, with the injection charging method, since the photosensitive member is electrically charged by directly applying current from the fibers, if a winding gap is generated, this part may not sufficiently electrically charge the photosensitive member. Hence, with the injection charging method, the density irregularity generated in an image may be increased as compared with the electrically discharging method.
As one of countermeasures for the winding-seam irregularity, there is suggested inclined-fiber processing in which tip ends of fibers of a roll brush are inclined and hence a gap is filled (see PTL 1).